By some (possibly dubious) measures, Broadway just got slightly, vaguely, sorta-kinda cooler. The Broadway musical version of Legally Blonde will be aired on MTV. That's not a five-minute segment in some uplifting special about stage-struck tweens chasing their Broadway dreams: it's the entire show.

Admittedly, securing that much airtime on MTV isn't quite the seal of zeitgeist approval that it would have been 20 or even 10 years ago. MTV has strayed from the actual music business, now retailing lots of reality TV (and not the fun kind). But to have a Broadway musical reach a nationwide audience behind an MTV logo seems a big deal indeed.

The first intriguing aspect of the deal is the Broadway producers' enthusiasm for it. Instinctively, you'd think that giving away your one asset - the show - would cannibalise the paying audience. But recent history suggests otherwise. In 2004, many a Broadway watcher wondered if the film version of Phantom of the Opera would finally, finally drive the masked one from New York. Three years later, it persists. Even now, the recent film version of Hairspray has pumped the Broadway version's numbers up to near capacity.

So if an audience enjoys the film version of a show, do they then feel the need to experience it in three dimensions? (Orson Welles' all-time definitive explanation of the limitations of film vis-à-vis theatre: "It comes in a can.") Another explanation for the box-office bump is that an unadventurous audience (largely tourists, these days), when choosing a Broadway show, opts for one they've already tested. This is the same depressing force that drives them, on their trips to the restaurant mecca of the western hemisphere, to dine at Times Square versions of the chain restaurants they've got back home.

But the demographics here seem just as compelling as the dollars and cents. Between Wicked (always sold out), Rent (resurgent, thanks to the return of two original stars), and the MTV fans likely to turn out for Legally Blonde, the health of the Broadway musical is growing more and more dependent on the tastes of a young audience. Creatively, this might turn out to be a pact with the devil. (The new revival of Grease, which was cast on a TV show and which seems tailored to ride that demographic wave, doesn't inspire much confidence.) But I'm inclined to be optimistic.

The best news of Broadway's summer is that Spring Awakening, Duncan Sheik and Steven Sater's rock version of Frank Wedekind's play about hormonal teenagers in trouble, defied its doubters and recouped its $6m investment. It did so, apparently, by making unprecedented use of the internet to build a fervent young following. Spring Awakening, for my money, is superior to Legally Blonde in almost every way: more propulsive music, sharper choreography, richer design, and a story that's much, much more mature. (So mature, in fact, that I doubt MTV could have gotten this show approved by George W Bush's FCC even if they tried.) So while a potential box-office windfall for Legally Blonde doesn't do much for me, the long-term prospect of having a bigger potential audience for the next Spring Awakening seems exciting indeed, no matter what Jonathan Franzen says.